Step size of the rotary proton motor in single FoF1-ATP synthase from a thermoalkaliphilic bacterium by DCO-ALEX FRET

TL;DR

This study uses advanced single-molecule FRET techniques to measure the step size and dynamics of the rotary Fo motor in a thermophilic ATP synthase, revealing high flexibility and temperature-dependent activity.

Contribution

It introduces a novel FRET-based method to analyze the rotary steps of a thermophilic ATP synthase, identifying smaller step sizes than previously known.

Findings

Identified 13 rotary steps in the thermophilic enzyme.

Discovered fast back-and-forth stepping indicating high flexibility.

Showed temperature and detergent dependence of motor activity.

Abstract

Thermophilic enzymes can operate at higher temperatures but show reduced activities at room temperature. They are in general more stable during preparation and, accordingly, are considered to be more rigid in structure. Crystallization is often easier compared to proteins from bacteria growing at ambient temperatures, especially for membrane proteins. The ATP-producing enzyme FoF1-ATP synthase from thermoalkaliphilic Caldalkalibacillus thermarum strain TA2.A1 is driven by a Fo motor consisting of a ring of 13 c-subunits. We applied a single-molecule F\"orster resonance energy transfer (FRET) approach using duty cycle-optimized alternating laser excitation (DCO-ALEX) to monitor the expected 13-stepped rotary Fo motor at work. New FRET transition histograms were developed to identify the smaller step sizes compared to the 10-stepped Fo motor of the Escherichia coli enzyme. Dwell time analysis revealed the temperature and the LDAO dependence of the Fo motor activity on the single molecule level. Back-and-forth stepping of the Fo motor occurs fast indicating a high flexibility in the membrane part of this thermophilic enzyme.